Process of esterifying mercerized cellulose with lower fatty acids



Patented Oct. 9, 1928. I

UNITED STATES;

PATENT OFF-ICE.

HANS T. CLARKE AND CARL J'. MALM, OF ROCHESTER, NEW YORK, ASSIGNOBS TOEASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEWYORK.

PROCESS OF ESTERIFYING MERCEBIZED CEELULOSE WITH LOWER FATTY ACI IDS.

No Drawing.

Tl is invention relates to. processes of esterifying mercerizedcellulose with lower fatty acids, preferably those containing more than1 and less than 8 carbon atoms.

One object of our invention is to provide an inexpensive and simpleprocess of producing cellulose esters of the lower fatty acids withoutthe aid of anhydrids or catalysts. Another object of the invention is toprovide a process of making cellulose esters of the lower fatty acids ina plurality of stages, certain of the'acid groups being combined intothe ester during the first stage without use of anhydrids'and catalysts,and the remainder of the acid groups being com bined in the ester by thesubsequent treatment of the esters formed in the first stage,thus'efiecting an economy in expensive ingredients, such as theanhydrids of the acids. Another object of the invention is to provide aprocess in which the first-stage esterificatlon is performed in theabsence of any material more hydrolytic than the fatty acids themselves,thus leaving the cellulosic material with the minimum moleculardegradation and essentially unchanged in its physical appearance by thefirst stage of the process; Other' objects will hereinafterappear.

In our application, Serial No. 122,028 filed July 12th, 1926 forcellulose esters of fatty acids and processes of making the same we haveshown that unmodified or undegraded cellulose can be esterified, underproper conditions, by the lower fatty acids without the use of catalystsor expensive anhydrids'. and the like. In the case of each of the lowerfatty acids, approximately one molecular proportion of acid is combinedwith an amount of cellulose corresponding to 24 carbon atoms. Thisfirst-stage ester is then esterified further by the'usual process,

but with notable economies in the use of anhydrids and with mildcatalysts to avoid molecular degradation. 7

We have now found that celluloseesters of the lower fatty acids may beprepared in which more than 2 molecular proportions of acid are combinedwith anamount of cellulose corresponding'to 24.- carbon atoms andwithout the use of anhydrids or atalysts,-

Application filed April 23, 1927. Serial No. 186,170.

in fact, with the minimum molecular degradation andwithout modifying thephysimercerized cellulose with the acids as the sole acylating agentsare very stable, as indicated by their resistance to splitting ofl'acetyl groups when tested by prolonged boiling in Water. In general thefibers of the new compounds are. superficially indistinguishable fromthe mercerized cellulose fibers from which they are prepared.

It is a useful fact that these esters are 'more readily esterified thanplain cellulose Moreover, it

or mercerized cellulose fibers. is necessary to add fewer acetyl groupsto them, since they already contain useful amounts. The practical effectis that when these esters are further esterified by using anhydrids, oreven acyl chlorides, in the ways previously described for the acylationof cellulose itself, savings of from 20 to 40% of the amount of anhydridor chlorid may be' obtained. A substantial saving is effected so long asour first-stage esters have more. than one acyl group for each 24 carbonatoms in the cellulose.

Our invention is concerned with the esters of the fatty acids havingmore than 1 and less than 8 carbon atoms, such as acetic, propionic,butyric, valeric, caproic, heptylic, etc. The rate of esterificationfalls off rapidly with the higher members of this series of acids.Consequently acetic' acid, propionic acid and butyric acid are thosewhich are preferred, because of their relatively greater commercialavailability and their greater speed of reaction. Acetic acid iscommercially the most important at present, because of its lower cost.

For the raw cellulose to be mercerized we can employ any of the typescustomarily used in the manufacture of esters such, for instance, ascotton, surgical cotton wool, tissue paper especially prepared fromcotton, and even sulfite wood" pulp, (preferably Ila:

bleached); Our process has a notable whitening tendency on the cellulosewhere the latter is initially colored, but the general appearance of thefibers is not changed. In

other words, they do not swell, gelatinize,

- or go into solution duringthe treatment with the fatty acids in thefirst stage.

The first-stage esterification may be conducted over a considerabletemperature range. In eneral we prefer to operate above 100 oftemperatures above 170 (3., because of the danger of molecularlydegrading the cellulose and the products produced from it.

- Within this preferred range the tempera- .a superatmospheric pressure,say in an autoclave', provided the corresponding temperav ture does notreach the point where the product is degraded. While we use the acidsasthe sole acylating agents'and prefer to employ tl1em.without admixturewith other liquids, nevertheless, the esterification can-beefi'ected,'when the acids-are mixed with non-acylating liquids, suchas'chloro form, carbon tetrachloride or benzene. But

these produce no marked advantage.

During the first-stage acylation it is desirable to keep the amount ofwater present very low.- The total water present, including the waterin: the original ingredients,

plus the water formed during the esterification, should never be allowedto reach the point where it prevents the introduction of more than 8% ofthe acyl-group. We aim to maintain the conditions during the reactionsuch that the water is removed or diminished in quantity. The use of afrac-. tlODfitlIl this res'u t,'the water vapor being allowed to columnis one way of obtaining pass outwhile the fatty acids are condensed Iand flowb'ack to the bath. This is possible because all of the fattyacids having more than 1 and less than 8 carbon atoms boil considerablyabove the boiling point of water. 1 ,7

The .mercerization pretreatment of the cellulose is along customarylines. For ex'-.

' ample, the 'me'rcerization may be conducte'd.

' at room temperature,- by simply nnmersin the cellulose; fibers in adilute solution of a kali, such as sodium hydroxid. The time ofmercerization, known as aging will be longer the more dilute thebath.With an 18% aqueous sodiumrhydroxid solution, we

have obtained satisfactory results u on stoppin the mercerization at theend 24 hours, ut no harm results when the merin order toinsurereasonably rapid action and we do not advise the useressure, aconsiderable excessof ace-noes ceriaation in such a solution has beencar.-

ried out for over 72 hours,--48 hours being a goodmedium time. Moreover,a merceri' zation in a 40% aqueous solution of sodium hydroxid for 24hours is effective and without harm to the molecule. After soaking inthe alkaline solution, the latter is drained oil and the mercerizedcellulose fibers washed free from alkali with water and dried in the airat to C.

If desired, the water may be removed by washing witha suitable organicliquid miscible with water, such as alcohol or acetone, previous todrying. Acetic acid may be employed, in which case air-drying isrendered unnecessary. The water may also be re moved by distillationwith a water-immiscible liquid of suitable boiling temperature, such asbenzene or carbon tetrachloride.

In the' first stage of esterification the mercerized cellulose, thusprepared, is heated in the acid until the acetyl group introduced in theester is at least 8% of the latter. For example, we may boil 1 part byweight 01" the mercerized cellulose in an excess of acetic acid, say 30to 40 parts by weight, the

operation being carried out'at atmospheric pressure. The acid isinitially substantially free from water, say of 99 to 100% strength,

The boiling. point of the reaction bath is thus'kept at about 117 C. orslightly above. Of course, any suitable precautions are taken to preventthe loss of-acid by loss of its vapor-s, the same being condensed andreturned to the bath by the use of any of the expedients familiar tochemists.

As the boiling in acetic acid is continued under these conditions theesterification pro-.

'gressively. takes place. Roughly the pro: portion of acetyl can becarried to well over 14% and even above 20% of the weight of the ester.This strong esterification may be obtained after different lengths oftime, according to the method b was dried. Some of them reachapproximately 14%: after 96 hours of treatment. But a useful muchshorter tune. For instance, the percentage of acetyl in the esterreaches 8 before 48 hours in practically every 1nstance and oftenreaches 11% in that time. This 8+% ester has. the property of beingreadily esterified further in t e usual baths 'but with very goodeconomy in acetic anwhich the cellulose I product is obtained after a.

acid? the relation being in-the' proportion of the molecular'weight ofthe acyl g'roup to the molecular weight of the acid. For 1nstance, 8% ofthe acetyl group means about 11.2% of combined acetic acid. 4 p

" parts by weight of propionic or The following table illustrates themanner in which acetic acid reacts with cotton cellulose which has beenmercerized, washed, and freed of water under different conditions:

Times of boiling in acetic acid.

No 0 Percentages of acetyl experi- 24 hrs. 48 hrs. 96 hrs. 200l1rs.300m. 400hrs. 500l1rs.

1 1.4 as 11.0 11.6 12.9 14.1 2 1.7 9.3 11.9 12.3 14.5 15.9 a 9.3 11.013.5 17.5 19.2 20.9 21.6 4 10.2 13.0 14.8 17.0 19.5 22.2 22.0

In experiment No. 1 the mercerization had been done in an 18% N aOHsolution for 48 hours at room temperature but it Was dried after Washingand before boiling in acid. In N o. 2 a solution of N aOH was used inmercerizing the fibers being finally dried as in N o. 1. But in Nos. 3and 4 after mercerizing, in 18% and- 40% -NaOH solutions respectively,for 48 hours at room temperature and washing out the free alkali,-' thewater Was removed from the fiber by repeated washing with glacial aceticacid. The mercerized fibers were thenboiled in acidwithout having beendried. Since No. 1 and No. 2 Were exactly parallel with,

No. 3 and N o. 4, except for the drying operation, it will be seen thatthe dehydration Without drying greatly speeds up the process, even morethan the useof a strong mercerizing solution, as in N o. 2 and No. 4.After this first-stage esterification, the excess of acid is removed ifthe ester is to be further esterified in a bath containing an anhydridand acatalyst. Part of the acid can, however, be left with tion as adiluent or a solvent during the sec end stage acylation, as is usual inthe ordinary acetylation of plain cellulose. If the acetylated fibers,from the first stage, are desired to be used in that condition, theyare, of course, thoroughly Washed in water and dried, in which event thelooklike the mercerizedfibersfrom which they were derived. Instead ofthe acetic acid in the above example, we may employ eqglimolecularutyric acid and employ, preferably, a fractionating column through whichthe water vapors may pass, While retaining the acid vapors. The time ofboiling -is conveniently about 200 hours. When 30 parts of heptylic acidare used with 1 part by weight of mercerized cellulose, the temperatureshould be kept below 165 C. and preferably above 145 C. This is underthe'boiling pointrof the acid, but sufficient to obtain a usefulesterificatihn without degradation.

When itis desired mospheric pressures,

to work at superat- 1 part of mercerized the ester to funccellulose maybe heated, for example, with 30 parts of acetic acid by weight 'of99 to100% strength at a temperature between 140 and 160 (3., say in a vesselof the autoclave acetic acid-conducted through the tube. This operationmay be conducted either at atmospheric pressure or subatmosphericpressure, provided the temperatures do not go above The excess of acidvapor may be repassed or slightly reheating, through the tube. enables arapid acetylation to take place. The subsequent esteri'fication of thefirststage esters can take place in any of the usual esterifying baths,but with the amount of anhydrid diminished by from 20 to 40%. Moreover,the increased susceptibility of our first-stage esters to furtheresterification enable: us to carry out the latter operation without theuse of strong catalysts, thus avoiding the danger of such catalysts assulfuric acid are employed. \Ve can operate with a milder and safer one,such as zinc chlorid or magnesium perchlorate trihydrate. As suchesterification methods have been previously described, it is unnecessaryto go over them in detail here.

Having thus described our invention, what We claim as new and desire tosecure by Letters Patent is:

1. In the process-of making a cellulose ester of a fatty acid,mercerizing the cellulose and thereafter heating together the mercerizedcellulose and a fatty acid having more than 1 and less than 8 carbonatoms without a catalyst at a temperature between 100 and 170 C.inclusive until the acyl group in the ester thus produced reaches atleast 8%,

ing a ent.

2. n the process of making cellulose acetate, mercerizing the cellulose,and heating together the mercerized cellulose and substantiallyanhydrous acetic acid without a catalyst above 100 C. and below 170 C.

recirculated, preferably after" This degradation when said acid beingthe sole acylatinclusive until the acetyl group in the ester thusproduced reaches at least 8%, said acetic acid being the soleacetylating agent.

3. In the process of making a fatty acid cellulose ester, *mercerizingthe cellulose, partially esterifying the. mercerized cellulose with afatty acid'having more than 1 less than 8 carbon atoms, inthe absence ofany anhydrid or catalyst, until there is and more than one acyl group inthe ester for each. 24 carbon atoms in the cellulose, and

thereafter esterifying it further with the aid of an anhydrid of a fattyacid and a catalyst. v

4;. In the process of making a fatty. acid cellulose ester, mercerizingthe cellulose, heating the mercerized cellulose with a fatty acid havingmore than 1 and less than 8 carbon atoms without. an catalyst until theacyl group inthe ester t us formed reaches at least 8%, said acid beingthe sole acylat-. ing agent, and thereafter further esterifying it withthe aid of an anhydrid of a fatty acid and a catalyst.

5. In the process of making cellulose acetate, mercerizing thecellulose, heatin the cellulose in an excess of acetic acid at atemperature between 100 and 170 C. in the absence ofa catalyst, the acidbeing the sole acetylating agent, until the acetyl group in the esterreaches at least 8%, and thereafter further acetylating the-ester thusproduced in the presence of acetic anhydrid and a milder catalyst thansulfuric. acid.

6. In the process of making a cellulose ester of a fatty acid,Inercerizing the cellulose in an aqueous alkaline solution, washing outthe alkaline solution from the cellulose with water, removing the waterfrom the cellulose with a substantially anhydrous organic liquid andheating the cellulose thus prepared with a fatty acid having more thanneeagoce l and less than 8 .carbon atoms in the absence of a catalyst ata temperature between 100 and 170 CL inclusive until the acyl group fromsaid acid in the ester thus produced reaches at least 8%.

' 7. In the process of making cellulose'acetate,merceriz1ng thecellulose in an aqueous alkaline solution, washing out said solutionwith water, washing out the water with glacial acetic acid, boiling thecellulose in:

glacial acetic acid without a. catalyst until the acetyl group in.reaches at least 8%, said acetic acid being the sole acetylating agent.

8. In the, process of making a cellulose ester of a fatty acid,mercerizing the cellulose in an aqueous alkaline solution, dehydratingthe cellulose with a substantially anhydrous organic liquid, and heatingthe cellulose thus prepared with a fatty acid, having more than 1 andless than 8 carbon atoms at a temperature between 100 and 170 C.inclusive in the absence of catalysts or an= hydrids, until more. thanone acyl group is esterified with the cellulose for every 24: carbonatoms in the latter. I

4 Signed at Rochester, New York, this 18th day of April, 1927.

. HANS 'r. CLARK. CARL .1. MALM.

the ester thus produced

